ABRASIVE ARTICLE HAVING A COLORED SUBSTRATE

Abstract: An abrasive article (10) including a colorant (16) applied to the substrate (11) which is visible through the abrasive medium (17) and which denotes the grade of the abrasive medium. The colorant (16) can be applied to the front side (14) of the substrate (11), and the abrasive medium (17) includes a make coat (18), size coat (20) and abrasive particles (22) which are light transmissive when applied to the substrate (11) over the colorant (16) such that the colorant (16) is visible through the abrasive medium (17). A method of making an abrasive article (10) having a colorant (16) applied to the substate (11) and visible through the abrasive medium (17) is also disclosed as is a system for identifying the grade of the abrasive article (10).

Description: ABRASIVE ARTICLE HAVING A COLORED SUBSTRATE BACKGROUND OF THE INVENTION The present invention relates to abrasive articles in which abrasive grains are bonded to a substrate. More particularly, the present invention relates to abrasive articles having a colorant on the substrate visible through the abrasive medium. On an abrasive art: le, it is known to place indicia in the form of printed information on the back side of the article opposite from the front side which comprises the abrasive grains or grit. The indicia typically includes a grade number, a product name or other identification. The grade number refers to the average particle size or the particle size distribution of the abrasive grain. Printing on the back side of some prior art abrasive articles is incidentally viewable from the front side due to the substrate being translucent. However, the information is not readable since it is in a mirror image. Such a product has been sold under the trade mark IMPERIAL MICRO FINISHING FILM by Minnesota Mining and Manufacturing Company. Abrasive articles are typically converted into a wide variety of forms such as sheets, discs, or belts. It is well known to attach the discs or sheets to a backup pad or support pad during use by means of a pressure-sensitive adhesive or other suitable means. When the indicia is disposed on the back side of the abrasive article, the information cannot be seen if the abrasive article is opaque. If the abrasive article is translucent, only a mirror image of the indicia is seen and it is difficult to discern the indicia. Information which cannot be read by viewing the front of the abrasive article has several disadvantages. First, an operator may want to check the particular grade of an abrasive article if the operator forgets which grade of abrasive article is being used when the abrasive article is attached to a back-up pad or support pad. Secondly, if a second operator or new operator uses the same abrasive article, the second or new operator may not know the particular grade of the abrasive article. In both instances, the operator has to remove the abrasive article from the pad in order to check the grade, the product identification or the manufacturer. Then, if possible, the abrasive article is remounted on the back of the pad. If not, then a new abrasive article has to be attached to the pad. Another disadvantage relates to packaging of the abrasive article. Generally, in order to check the grade of the abrasive article, an abrasive article has to be removed from the package in order to view the indicia containing the grade designation. U.S. Patent 4,437,269 discloses an abrasive sheet having indicia carried on its rear face overlaid by a translucent textile material providing a surface engagable by hooks. The material being adhered to the indicia and information content remain discernible through the textile materials. U.S. Patent 5,137,542 discloses a coated abrasive article with a reduced tendency to accumulate static electric charge during the abrading of an electrically insulating workpiece, said coated abrasive article having a backing having a front surface and a back surface, an abrasive medium comprising one or more layers bonded to said front surface of the backing and a pattern of continuous coating of a cured electrically conductive ink which may be positioned on either side of the backing, between layers of the abrasive medium or on top of the abrasive medium. Examples of electrically conductive materials incorporated into the inks include graphite, _rbon black, metals and metal alloys. Accordingly, the inks are black. Contrasting indicia can be printed over a continuous coating of cured electrically conductive ink printed over the exposed surface of the backing. U.S. 4,328,274 discloses a friction sheet material which may be adherently bonded to the patterned surface of a substrate which permits the visual observation of such pattern when attached. The friction surface sheet material comprises a backing layer formed of a dimensionally stable polymeric film such as polyethylene terephthalate. A first and second coating of the first and second transparent binder material adherently bond a multitude of minute transparent glass particles uniformly dispersed over the upper major surface of the backing layer, with the tops of the glass particles projecting above the binder coating to provide a friction surface, and the bottom major surface of the backing layer as thereon a layer of transparent pressure-sensitive adhesive. PCT Application No. US93/01789, corresponding to U.S. Patent Application Nos. 07/868,007 and 08/077,315, discloses an abrasive sheet having a substrate with a front and back side. An abrasive material is adhered to the front side of the substrate. Indicia are disposed on the substrate and are viewable from the front side of the substrate in a normal non- mirror image readable from left to right. In one embodiment, the indicia are disposed on the back side of a substrate that is light transmissive. In another embodiment, the indicia are disposed on the front side of a substrate which may or may not be light transmissive. The indicia may be applied by conventional printing methods, e.g. letterpress, lithographic, gravure and screen printing methods. It is known to coat opaque abrasive on colored paper, e.g. brown paper. An abrasive sheet is also known comprising yellow paper having a black coating beneath an abrasive medium. It is also known to color the coated abrasive by incorporating pigment or dye into one or more of the coating layers. The colored abrasive material can serve as product identification by utilizing different colors for different grades of abrasive or as a brand image with a particular color being associated with one manufacturer. Coloring the coating layers of abrasive materials has several disadvantages. It is necessary to ensure compatibility between the colorant and materials of the coating layers to ensure the performance of the abrasive material is not deleteriously affected. The addition of colorant increases the cost both in terms of raw materials and waste disposal costs. Furthermore, changing the color of adhesive or other coating on the coating equipment is time consuming since it is necessary to thoroughly clean the equipment to avoid color contamination. Thus, color changes for small scale product volumes can be disproportionately expensive. There is a demand for a simple, versatile method for producing colored abrasive articles. SUMMARY OF THE INVENTION According to the present invention there is provided an abrasive material comprising a substrate having a front and back side with an abrasive medium provided on the front side of the substrate in which the abrasive medium is light transmissive and a colorant is present on the front side of the substrate beneath the abrasive medium whereby the colorant is visible through the abrasive medium. The present invention also provides a simple and effective method of imparting color to the abrasive side of an abrasive sheet. BRIEF DESCRIPTION OF THE DRAWING FIGURE 1 is a cross-sectional view of an abrasive article having a colored substrate according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An abrasive article 10 constructed in accordance with the present invention is illustrated in Figure 1. Colorant 16 is applied to the backing material or substrate 11 and thereafter overcoated with a translucent abrasive medium 17, including, for example, make coat 18, size coat 20, and abrasive particles 22. The colorant 16 may be applied in the form of a continuous coating, deposited image-wise, pattern-wise, or in the form of indicia. A plurality of different colors may be applied. In this manner, it is readily possible to obtain single color abrasive materials comparable to those obtained by pigmenting the abrasive medium, abrasive materials having printed information or indicia which may be viewed through the abrasive medium or any other color image or pattern may be applied and viewed through the abrasive medium. It is readily possible to print product information, advertising or promotional material, graphics etc. which may be viewed through the abrasive material. The colorant 16 may be applied by known coating and printing techniques and may readily be incorporated into existing processing machinery for manufacturing the abrasives. For example, a printing station may be incorporated prior to the coating station for abrasive medium and can print or coat the desired colorant. The color and/or image may readily be altered at the printing station without necessitating change of the backing material 11 and/or conditions of the station for coating the abrasive medium 17. Thus, it is readily possible to manufacture small scale product volumes having different colorant and/or image without alteration of the abrasive medium coating process. The term "colorant" used herein refers to any substance or material imparting a color other than black. The colorant 16 generally comprises a dye or pigment. In order to be visible the colorant must be selected to contrast with the color or shade of the opaque substrate 11. Thus, if the substrate 11 is itself colored, e.g. yellow, the applied colorant 16 is selected to provide a contrast, e.g. red. The substrate 11 is preferably opaque and may be selected from any of the materials which are known for use in the preparation of abrasive articles, including for example, paper, board, sponge, polymeric film, fiber, cloth, treated versions thereof, or combinations thereof. Preferred materials are paper, particularly A weight to F weight papers. The colorant 16 may be applied in the form of inks by any known printing techniques, e.g. letter¬ press, lithographic, gravure, and screen printing. However, any other ink printing technique may be employed including spraying, pens including felt tip marking pens, ink jet printing etc. Alternatively, colorant 16 may be applied by powder deposition e.g. powder coating or electrostatic coating or by hot melt deposition. Thus, in addition to printing techniques used for large volume printing, print technologies for smaller volume applications may be employed, e.g., computer controlled laser jet or ink jet printing, color photocopying, photographic, free-hand, stencil and hand-stamping techniques. The colorant 16 may optionally be included in a coating composition to form a colored barrier layer, colored primer layer or a colored anti-static layer. The abrasive medium 17 is normally prepared by coating one surface 14 of a substrate 11 with a first binder layer 18 having adhesive properties, often referred to in the art as the "make". Particles or abrasive material 22 are applied to the coated substrate and partially embedded therein. A layer of a second binder 20, often referred to as the "size", is then applied to the material. The thickness of the second binder layer 20 regulates the amount of the abrasive material 22 extending abo * the binder medium. Anti-loading materials may be included in the size or in a further optional layer, referred to in the art as the supersize (not illustrated) . The binder or adhesive used in the make 18 or size 20 is light transmissive to enable the viewing of the colorant 16 through the abrasive medium 17 under normal room lighting conditions. Examples of typical adhesives include polyester resins, urethane resins, acrylate resins, phenolic resins, animal glue, urea- formaldehyde resins, melamine resin, epoxy resin and mixtures thereof. Such adhesives are applied at a thickness normally used for adhering abrasive materials 22 to a substrate 11. Preferably, the abrasive grains 22 should also be light transmissive. Examples of typical abrasive grains 22 used for abrasive material include silicon carbide, silicon dioxide, aluminum oxide, white aluminum oxide, ceramic aluminum oxide, cerium oxide, diamond, cubic boron nitride, boron carbide and mixtures thereof. Although typical abrasive grains 22 are somewhat opaque, the particles 22 as a layer on the substrate 11 still have light transmissive properties such that the colorant 16 of the present invention clearly shows through the abrasive medium 17. Furthermore, in abrasive articles 10 in which the abrasive grains 22 are spaced from each other (sometimes referred to as "open coat") , the opacity of the individual abrasive grains 22 is even less of an obstruction to viewing the colorant 16. Translucent abrasive grains 22 are preferable, such as white aluminum oxide, to aid in the viewing of the colorant. The abrasive articles 10 of the invention may take a variety of forms, e.g. sheets, discs, belts etc. The back 12 of the substrate 11 may comprise means for releasably securing the article to a support pad, e.g. a pad of a sanding machine. Such means may comprise a pressure-sensitive adhesive or one part of a hook-and- loop fastening system. The invention will now be illustrated by the following Example: EXAMPLE The following opaque substrates 11 were used: Latex saturated paper - waterproof from Kimberly Clark, Kraft abrasive base papers from Arjo- Wiggins, Office bond - Lanier Natura 95 white paper. Ensign 80g/m 2 - pink paper. The following colorants 16 were employed: Aultopake white ink from Sun Chemicals, Artliner office ink pad - red, Rosetto Quickspray Marking ink - white and red. Nobo felt tip marking pens, various colors. Hewlett Packard Desk Jet 550C color printer and Hewlett Packard Paint Jet XL300 printer controlled by "Harvard Graphics" and Freelance for Windows 2.0 software 16 x 16 matrix of library colors, with standard color print cartridges. The following abrasive media 17 were used: Phenol formaldehyde based abrasive media 18, 20 having aluminum oxide abrasive particles 22 which are currently present on abrasive sheets commercially available from Minnesota Mining and Manufacturing Company under the trade name 3M 314 (grades P800, P400 and P200) . Phenol formaldehyde based abrasive medium 18, 20 having silicon carbide abrasive particles 22 which are currently present on abrasive sheets commercially available from Minnesota Mining and Manufacturing Company under the trade name 3M 734 (grade P60) . Urea formaldehyde based abrasive medium 18, 20 having aluminum oxide abrasive particles 22 which are currently present on abrasive sheets commercially available from Minnesota Mining and Manufacturing Company under the trade name 3M 212 (grades P180 and P80) . Samples were prepared by applying one or more of the above colorants 16 to the above opaque substrates 11 which were then overcoated with one of the abrasive media 17. In each case the color showed through the abrasive medium.

Claims: WHAT IS CLAIMED IS: 1. An abrasive article comprising: a substrate; a colorant provided on a surface of said substrate; and an abrasive medium provided on said surface of said substrate over said colorant; wherein said abrasive medium is light transmissive, said colorant is visible through said abrasive medium, and said colorant denotes the grade of said abrasive medium. 2. An abrasive article as in claim 1, wherein said substrate is opaque. 3. An abrasive article as in claim 1, wherein said colorant is coextensive with said surface of said substrate. 4. An abrasive article as in claim 1, further comprising a primer layer on said substrate, wherein said primer layer includes said colorant. 5. An abrasive article as in claim 1, further comprising a barrier layer on said substrate, wherein said barrier layer includes said colorant. 6. An abrasive article as in claim 1, further comprising an anti-static layer on substrate, wherein said anti-static layer includes said colorant. 7. An abrasive article as in claim 1, further comprising a plurality of colorants provided on said surface of said substrate wherein said plurality of colorants denotes the grade of said abrasive medium. 8. A system for identifying the grade of an abrasive article, comprising: a first abrasive article including: a first substrate including a first surface; a first colorant provided on said first surface; and a first abrasive medium provided on said first surface over said first colorant, wherein said first abrasive medium has a first grade, and; a second abrasive article including: a second substrate including a second surface; a second colorant provided on said second surface; and a second abrasive medium provided on said second surface over said second colorant, wherein said second abrasive medium has a second grade; wherein said first and second abrasive media are light transmissive such that said first and second colorants are viewable through said first and second abrasive media, respectively; and wherein said first colorant denotes said first grade and said second colorant denotes said second grade, thereby differentiating said second abrasive medium from said first abrasive medium and identifying said grades of said abrasive articles. 9. A system for identifying the grade of an abrasive article as in claim 8, wherein said first and second substrates are substantially opaque. 10. A system for identifying the grade of an abrasive article as in claim 8, wherein said first colorant is coextensive with said first surface and said second colorant is coextensive with said second surface. 11. A system for identifying the grade of an abrasive as in claim 8, wherein: said first abrasive article further includes a first plurality of colorants provided on said first surface; and said second abrasive article includes a second plurality of colorants provided on said second surface; wherein said first plurality of colorants denotes said first grade and said second plurality of colorants denotes said second grade, thereby differentiating said second abrasive medium from said first abrasive medium and identifying said grades of said abrasive articles. 12. A method of making an abrasive article including a colored substrate, comprising the steps of: i) providing a substrate having a surface; ii) depositing a colorant on said surface; and iii) coating a light transmissive abrasive medium on said surface over said colorant; wherein said colorant denotes the grade of said abrasive medium. 13. A method as in claim 12, wherein said substrate is opaque. 14. A method as in claim 12, wherein said depositing step includes depositing said colorant as a layer coextensive with said surface. 15. A method as in claim 12, wherein said depositing step includes depositing a plurality of colorants on said substrate, wherein said plurality of colorants denotes the grade of said abrasive medium.

Inventors: CARTER CHRISTOPHER J, FRANCIS DAVID J, HENNEY ANTHONY J, SELLARS ADRIAN P, SWINNERTON RICHARD F, CARTER, CHRISTOPHER, J., FRANCIS, DAVID, J., HENNEY, ANTHONY, J., SELLARS, ADRIAN, P., SWINNERTON, RICHARD, F.
Applicants: CARTER CHRISTOPHER J, FRANCIS DAVID J, HENNEY ANTHONY J, MINNESOTA MINING & MFG, SELLARS ADRIAN P, SWINNERTON RICHARD F, CARTER, CHRISTOPHER, J., FRANCIS, DAVID, J., HENNEY, ANTHONY, J., MINNESOTA MINING AND MANUFACTURING COMPANY, SELLARS, ADRIAN, P., SWINNERTON, RICHARD, F.
Application year: 1994
Main classification: B24D3
IPC codes: B24D3, B24D11